Aging contributes to lung emphysema and progressive airway obstruction due to decreased elastic recoil. The aging process is also associated with cellular senescence-a state in which cells are metabolically active, but permanently unable to divide. Cigarette smoking is a major cause of lung emphysema by accelerating the aging process with resultant premature death due to atherosclerotic diseases and malignancy. Werner's syndrome, a genetic disorder caused by loss-of-function mutations in the Wrn gene encoding a member of RecQ helicase family (WRN protein), also accelerates aging. Both cigarette smoke and WRN protein defects induce cellular senescence. However, there have been no studies that investigate the potential link between cigarette smoke-induced accelerated aging and Werner's syndrome. I recently demonstrated that cigarette smoke induces cellular senescence via WRN protein downregulation in cultured human lung fibroblasts. I also showed that cigarette smoke decreases WRN protein in an ubiquitin-proteasome dependent pathway. The unique polypeptide sequences enriched in proline (P), glutamic acid (E), serine (S) and threonine (T) (PEST) residues are often targeted for protein degradation. By database analysis, I identified that WRN protein harbors three high value PEST targets. My proposed research will further investigate molecular mechanisms of cigarette smoke-induced cellular senescence via reducing WRN protein stability. My central hypothesis is that WRN protein stability serves as a critical mechanism that alters lung susceptibility to smoking-induced emphysema. In Aim1, I will investigate the role of PEST sequences in cigarette smoke-induced WRN protein degradation and cellular senescence. In Aim2, I will determine if WRN protein defects alter the effects of cigarette smoke on cellular senescence and emphysema by using Wrn knock-out mice. This proposal will help to understand the potential role of WRN protein in smoking-induced emphysema and may contribute to novel therapeutic strategies directed at modulating WRN protein expression. PUBLIC HEALTH RELEVANCE: We have recently demonstrated for the first time that cigarette smoke induces cellular senescence via Werner's syndrome protein downregulation in cultured lung fibroblasts. We have also demonstrated that cigarette smoke enhances WRN protein degradation in a ubiquitin-proteasome dependent manner. We propose in this application to identify the molecular mechanisms for WRN protein degradation after cigarette smoke exposure and to further investigate a role or WRN protein in cigarette smoke-induced cellular senescence and emphysema by using a murine model.